The present invention relates to the field of audible alarm devices in general, and in particular to that class of audible alarms that utilizes a driven vibrating member in conjunction with a resonance chamber to produce a loud sound roughly at a system resonant frequency and/or its multiples. The disclosed invention provides a general method for significantly improving the efficiency of sound production of such audible alarms, and it demonstrates several means for achieving such energy efficiency through example devices whose shape, structure and construction enable the realization of the method.
The audible alarm is one of the most ubiquitous of all devices, and its manifestations range widely from the “clang” of a church bell to the “shriek” sound of a siren to the “click” sound of a tactile keyboard switch. It is a fundamental objective of all audible alarms to provide the loudest, most recognizable sound possible; it is also desirable to produce such sound with the lowest possible expenditure of energy, i.e. to function efficiently.
One very large class of audible alarms, herein referred to as a “plate and chamber” alarm, is characterized by a mechanical, vibration “plate” which works in companion with an acoustic resonance “chamber”. These alarms commonly find application in such familiar devices as smoke detectors and/or carbon monoxide detectors, open door enunciators, vehicle backup warning devices, and automotive horns. Such alarms often use battery power as their primary or backup source of power, and the amount of available energy stored in the battery can be a limiting factor for the overall performance of the alarm. In battery-powered alarms in particular, it is highly desirable to convert the input power available to the alarm into the maximum amount of acoustic output power, i.e., for the alarm to be as energy efficient as possible. Thus it is highly desirable to obtain increased acoustic efficiency, either as an increase in loudness, a decrease in power, or a combination of both.